<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<SCRIPT>
    var obj={
        a:"xxx"
    }
    Object.defineProperty(obj,"b",{
        value:"b"
    })
    console.log(obj.propertyIsEnumerable("a"))
    console.log(obj.propertyIsEnumerable("b"))

    console.log(Object.keys(obj))
</SCRIPT>
</html>